This invention relates to a method of mitigating stress which occurs in a terminal user of a video display terminal (VDT).
The video display terminal (VDT) is also called a visual display terminal. The VDT is used as name generically of display devices, for example, cathode-ray tube (CRT) display for a television, for a video tape recorder, and for a computer, a liquid crystal display for a television game and so on. The VDT has a display screen on which a video signal is displayed.
As is well known in the art, the video signal represents successive pictures each of which may corresponds to a frame of the input video signal when the input video signal is, for example, a television signal. Each picture or frame consists of a plurality of picture elements (pixels).
As is well known in the art, stress disease occurs in the terminal user of the VDT by continuously seeing for a long time interval the display screen of the VDT on which the video signal is displayed. Such stress disease is called VDT stress disease. To prevent or mitigate the VDT stress disease, various implements to cover the display screen have been already proposed and used. Such implements are called stress mitigating implements. The stress mitigating implements are, for example, a filter with low index of reflection or an electrostatic preventing filter. These stress mitigating implements are effective to reduce the VDT stress disease of the terminal user in employment environment so that the display screen of the VDT displays the video signal representative of pictures which are practically at rest. Such displayed pictures are called pseudo-still pictures which are, for example, pictures displayed on the display screen when a document is prepared by using a word processor or a personal computer loaded with a word processing program.
Recent developments in computer graphics (CG) technique or virtual reality technique have made it possible to display various images (moving pictures) on the display screen such as a television screen or a computer display screen. Such images frequently include the moving pictures where a glaring figure moves quickly or flashes on and off hard. Such moving pictures whose luminance temporarily changes violently are very effective to draw attention of the VDT user who sees the moving pictures. On the other hand, such moving pictures whose luminance temporarily changes violently put a lot of stress on the VDT user. Many opportunities of seeing on the television screen or the computer display screen stimulative moving pictures processed by the CG technique and so on result in a new type of VDT stress disease. Accordingly, a prevention of the new type of the VDT stress disease is demanded. However, the new type of the VDT stress disease cannot be effectively prevented by using the above-mentioned conventional stress mitigating implements that improve a static characteristic of the picture display device. As a result, an effective means of its prevention is required.